An assembly of electromechanical devices used during orthopaedic computer assisted surgery (CAS) as a functional extension of the surgeon for precise procedural movement and placement (navigation) during the procedure (e.g., placement of a pedicle screw in spinal surgery). It is computer-based and typically consists of, e.g., an operator's console and a video camera used to track the instrumentation. The input to the computer is usually by means of an existing CT or MRI scan that is used as a template. The system tracks the instrumentation by reading the location points giving a three-dimensional (3-D) picture of the instrument's position/angulation. It can also be used as a training aid.